1. Field of the Invention
The present invention relates to a flying optical recording/playback head for information-recording/playing back by flying and running relatively above the medium surface of an optical recording medium capable of recording and playing back, in particular, an optical recording medium for recording, reproducing and erasing information by changing the optical characteristics or the magnetic characteristics of the recording layer by laser beams, and a method for controlling the flying height of the head.
2. Discussion of Background
A magneto-optical recording medium is a portable recording medium permitting large volume/high density recording, for which demands have rapidly been increasing for a large volume file or a rewritable medium for recording dynamic images for a computer in current fashion of multimedia.
The optical recording medium generally comprises a transparent circular disk-like substrate of a plastic material or the like on which a multilayer including a recording layer is formed, and in which recording and erasing are carried out by irradiating laser and playback is carried out by reflection light of laser.
Conventionally, laser for recording and playback was irradiated to the recording layer through the substrate. Recently, a technique for bringing the optical head closer to the recording layer to record and playback, a so-called near-field optical recording has been noted as means for increasing the density of recording (Appl. Phys. Lett. 68, p.141 (1996)). In this recording method, a solid immersion lens (hereinbelow, referred to as SIL) head is used to reduce the size of the laser beam spot, whereby it is possible to playback by a shorter mark determined by a laser wavelength (xcex) of a light source (xcx9cxcex/2NA: NA represents a numerical aperture of an objective lens), and therefore, recording and playback can be realized at a superhigh recording density. In the near-field optical recording, it is necessary to bring the optical head closer to the recording medium (xcx9c100 nm). Accordingly, unlike laser beams which are irradiated to the recording layer through the substrate as in the conventional magneto-optical recording medium, a method for irradiating directly laser beams to the recording layer without passing through the substrate is used. In this case, a flying type slider head is often used in order to bring the SIL head closer to the recording layer.
The flying type slider head is so adapted that a buoyant force is produced at the air-bearing slider by a flow of air caused by a movement of the recording medium, whereby the head runs above the surface of the recording medium. Since a flying height produced by the air-bearing slider generally depends on a moving speed of the recording medium, control of the flying height is possible by controlling the number of revolutions of a disk-like recording medium. However, there is a problem that the flying height varies depending on a position (in radius) on the recording medium if the number of revolutions is constant. In this connection, an attempt that the flying height is kept constant over the entire surface of the disk-like recording medium by contriving the shape and so on of the slider plane of the air-bearing slider so that dependency of the flying height on the moving speed is eliminated.
On the other hand, a slider head used for optical recording and playback generally has air-bearing sliders at both edges and an optical element such as SIL or the like at the center of a region interposed between the two air-bearing sliders. The size of the slider head is usually about several mm, and the size of the air-bearing sliders is from about the same to {fraction (1/10)} as large as the head. On the other hand, the size of a photo-coupling region existing in the lowermost plane of the SIL head is about 1 xcexcm. Accordingly, if the surface of the optical recording medium is not flat, a flying height of a photo-coupling portion (the distance between the photo-coupling portion and the surface of the optical recording medium opposing thereto) where the photo-coupling region exists is not always constant even when the flying height of the air-bearing sliders themselves is constant. In particular, since the flying height of the photo-coupling portion is very small as 100 nm or less, there is substantial influence on the flying height of the photo-coupling portion even though the radius of curvature of projections and recesses in the surface of the optical recording medium is about several m. Further, the flying height of the air-bearing sliders themselves is different from the flying height of the photo-coupling portion above the projections and recesses even when the two-dimensional spread of the projections and recesses in the surface of the optical recording medium is about from several ten to several hundred xcexcm.
The optical recording medium is generally fabricated by using a substrate obtained by injection-molding resin such as polycarbonate or the like. However, it is difficult to form a substrate having a completely flat plane because of variation of the shape of a stamper used for the injection-molding and conditions of shaping, and therefore, there is a curve in the substrate surface in its entirety or projections and recesses having a spread of about several ten to several hundred xcexcm in the substrate surface.
On the other hand, in the near-field optical recording, the intensity of a playback signal largely depends on a flying height of the photo-coupling portion, i.e., a photo-coupling gap (the distance between the photo-coupling portion and the surface of the optical recording medium opposing thereto). Accordingly, even when the flying height of the air-bearing sliders themselves can be kept constant, the size of the photo-coupling gap varies whereby it is difficult to obtain a stable playback signal.
From such reasons, there was a problem that a stable flying height of the photo-coupling portion of the flying type slider head could not be obtained by controlling only the shape of the air-bearing sliders of the flying type slider head or controlling only the moving speed of the optical recording medium. Accordingly, the playback signal was deteriorated.
An object of the present invention is to provide an optical recording/playback head for near-field optical recording/playback which can, for example, keep the distance between an optical lens such as SIL or the like and a recording medium, namely, the flying height of an optical element such as the optical lens or the like to be constant to thereby obtain a playback output stably.
The inventor of this application has made intensive study in view of the above-mentioned circumstances and has achieved the present invention.
Namely, the flying optical recording/playback head of the present invention is a flying optical recording/playback head having a slider for producing buoyancy by a movement of an optical recording medium and an optical element for irradiating light for information-recording and/or playback to the optical recording medium, which is characterized by comprising a device for controlling the relative position between the slider and a nearest surface of the optical element which is nearest to the optical recording medium (hereinbelow, referred to as the nearest surface of the optical element). In particular, there is provided a flying optical recording/playback head wherein control for the relative position is carried out by a thermal expansion or a piezoelectric effect of an optical element supporting member for holding the optical element on the slider, or a thermal expansion of at least a portion of the optical element.
Further, the flying optical recording/playback head of another aspect of the present invention is a flying optical recording/playback head having a slider for producing buoyancy by a movement of an optical recording medium and an optical element for irradiating light for information-recording and/or playback to the optical recording medium, which is characterized in that the optical element has a photo-coupling portion having a flat plane substantially parallel to the surface of the optical recording medium at a side opposing the optical recording medium, and a device for controlling the relative position between the photo-coupling portion and the slider is provided. In particular, there is provided a flying optical recording/playback head wherein the optical element is provided with a cylindrical projection projecting toward the optical recording medium in its surface opposing to the optical recording medium, and the photo-coupling portion is formed of a flat plane substantially parallel to the surface of the optical recording medium, the flat plane being at the end of the cylindrical projection, whereby the relative position between the slider and the photo-coupling portion is controlled based on a thermal expansion of the cylindrical projection. Further, it is preferable that a thin layer having an electric resistance is formed on the side surface of the cylindrical projection, whereby the relative position between the slider and the photo-coupling portion is controlled by controlling power supplied to the thin layer having an electric resistance.
The flying type optical recording/playback head of another aspect of the present invention is characterized by a flying optical recording/playback head having a slider for producing buoyancy by a movement of an optical recording medium and an optical element for irradiating light for information-recording and/or playback to the optical recording medium, wherein the optical element attached to the slider has a flat plane at a light emitting side; a cylindrical projection projecting in a cylindrical form is formed in a portion of the flat plane; and a thin layer having an electric resistance is formed on the side surface of the cylindrical projection, whereby the distance between the photo-coupling portion comprising the end plane of the cylindrical projection and the optical recording medium is controlled by utilizing a change of the shape of the cylindrical projection due to a thermal expansion, which is caused by supplying power to the thin layer having an electric resistance.
Further, the method for controlling the flying height of the flying optical recording/playback head of the present invention is a method for controlling the flying height of the flying optical recording/playback head characterized in that photo-coupling gap as the distance between a nearest surface of the optical element, i.e., a photo-coupling portion and the surface of the optical recording medium is detected, and the relative position between the nearest surface of the optical element, i.e., the photo-coupling portion and the slider is changed by utilizing a fluctuation quantity with respect to a reference value obtained by the detection to thereby control the photo-coupling gap to be constant. Further, in the method for controlling the flying height of the flying optical recording/playback head, it is preferable that the size of the photo-coupling gap is detected by an intensity of returning light from the optical element and the optical recording medium.
The optical element in the present invention is, for example, an optical lens, a hemi-spherical solid immersion lens, or an optical fiber having a tapered portion thinned toward its end.
More specifically, the present invention relates to a flying optical recording/playback head having a slider for producing buoyancy by a movement of an optical recording medium and an optical lens for irradiating light for information-recording and/or playback to the optical recording medium, characterized in that a device for controlling the relative position between the slider and an optical lens is provided, e.g., a flying optical recording/playback head having a device utilizing either effect of heat or a voltage in order to change the relative position between the slider and the optical lens. Namely, a thermal expansion or a piezoelectric effect of an optical lens supporting member for holding the optical lens on the slider is used. Further, the method for controlling the flying height of the present invention is a method for controlling the flying height, characterized in that a photo-coupling gap as the distance between the optical lens and the optical recording medium (a flying height of the optical lens) is detected, and the relative position between the optical lens and the slider is changed by utilizing a fluctuation quantity with respect to a reference value obtained by the detection to thereby control the photo-coupling gap to be constant.